Fractional order PID controller for depth control of autonomous underwater vehicle using frequency response shaping approach

The increased need for underwater robotic systems for exploration of underwater resources has resulted in the development of advanced control systems and technologies to overcome the inspiring issues of underwater navigation and control. Improvement of efficient control schemes for underwater robots to manoeuvre in the constrained environments, overcoming the external disturbances, has been a real challenge to researchers. This paper deals with the development of tuning a fractional order PID controller by loop shaping approach for controlling the depth of an Autonomous Underwater Vehicle (AUV). The dynamics of AUV constitutes highly non-linear and unstable performance. The dynamic model of AUV is linearized for the depth system model. The fractional order PID controller tuning is done affording system gain margin and phase margin specifications. The unstable systemis stabilized using conventional PID controller and thenusing fractional order PID controllerfrequency response reshaping done in order to achieve required specifications.